Testing RO Water TDS Using a TDS Meter | Guide

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If you want to verify the TDS levels of your reverse osmosis water, the most straightforward way is to use a TDS meter.

This is a simple device that allows you to check your current situation in no time, and can help you maintain consistent readings over a long period of time if you take frequent measurements.

How to test RO water using a TDS meter, though? Find out below!

Key Takeaways

Here is how to test RO water TDS using a TDS meter:

  1. Take a water sample without contaminating it.
  2. Insert the TDS meter into the water and swirl gently.
  3. Wait for the number on the display to stabilize before reading.

How to Test RO Water TDS Using a TDS Meter

To test your reverse osmosis water with a TDS meter, simply follow these steps.

  1. Take a sample of your RO water. Use a container like glass that’s not prone to leaching, and make sure to avoid contaminating water with anything in the process. For example, if you’re taking your sample outdoors, make sure to keep dirt and other debris out of the sample.
  2. Take your TDS meter and remove its bottom cover.
  3. Turn on the TDS meter by pressing the button.
  4. Gently insert the tip of the meter into the water, making sure not to insert it too deeply – the device is not designed to be submerged below a certain level!
  5. Swirl the meter around gently to remove any bubbles from the water.
  6. Wait for the number on the display to stabilize (if there are any fluctuations). Once it does, it will show you your current TDS level.

tds meter in glass of water

How to Test RO Membrane Performance

Verifying the performance of your reverse osmosis membrane involves checking multiple factors, including the permeate flow rate, pressure drop, rate of recovery, discoloration, and even smell.

But by far the most important figure to consider is the TDS rejection rate of the membrane. If it goes below 80%, then your membrane needs to be replaced as soon as possible.

Reverse Osmosis Performance Formula

To calculate the salt rejection rate of your reverse osmosis membrane, you need to take two TDS measurements: One from a filtered sample, and one from an unfiltered one. Then, simply plug those numbers into this formula:

TDS rejection rate % = (TDS of unfiltered water – TDS of filtered water) / TDS of unfiltered water X 100

What Is Water TDS and Why Measure It?

TDS stands for total dissolved solids, and it’s an indicator of the concentration of solids in your reverse osmosis water, as the name implies. It’s an important measure, because it indicates the overall performance of the reverse osmosis membrane/system.

If the TDS levels of your filtered water go up too much, this likely hints at a problem with the operation of your reverse osmosis membrane, or the system overall.

If you have any questions about testing RO water with a TDS meter please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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